Many different sound insulation materials are available in the art. These materials have been used in a variety of applications, for example, to reduce noise from appliances, within buildings, from HVAC systems, within vehicles and the like. The selection of a particular sound insulation material is governed by several factors, including cost, thickness, weight and the ability to attenuate sound. Sound insulation attenuates sound by either absorbing sound waves striking the insulation or reflecting such sound waves outwardly and away from a receiving area. Sound attenuation is measured by the ability of a material to absorb incident sound waves (sound absorption) and/or by the ability of the material to reflect incident sound waves (transmission). Ideally, a sound attenuation material has a high sound absorption coefficient and/or a high transmission loss value.
Conventional sound insulating materials include materials such as foams, compressed fibers, fiberglass batts, felts and nonwoven webs of fibers. Of the nonwoven webs of fibers, meltblown fibers have been widely used in sound insulation materials. In addition, laminates of meltblown nonwoven webs have been used as acoustical insulation. In these prior uses of meltblown nonwoven webs in acoustical insulation, the meltblown nonwoven web typically was a relatively thick, low density layer of meltblown fibers, usually having a thickness of at least 5 mm and a density less than 50 kg m3.
Examples of such meltblown containing acoustical insulation are described in U.S. Pat. No. Re 36,323 to Thompson et al.; U.S. Pat. No. 5,773,375 to Thompson et al.; U.S. Pat. No. 5,841,081 to Thompson et al. These patents teach laminates containing meltblown fibers; however, the laminates have the problem of dimensional stability, meaning that the laminate does not retain its shape during handling, including compaction of the fibers and tearing or breaking of parts molded out of this material.
Another acoustical insulation containing meltblown fibers is described in U.S. Pat. No. 6,217,691 to Vair et al. In this patent, a mat of meltblown fibrous insulation is produced from meltblown fibers having a mean fiber diameter of less than 13 microns, a density less than about 60 kg/m3, preferably less than about 50 kg/m3, and a thickness between 3 and 20 mm. In the production of acoustical insulation, the fibers at least one of the top and bottom surfaces of the meltblown are melted to form a thin integral skin. The resulting material is then point bonded to provide integrity to the mat. In addition, the integral skin layer is perforated to provide air permeability to the mat.
In U.S. Pat. No. 3,773,605 to Pihlilstrom, an acoustical insulation material is produced by fusing and integrating several layers of a meltblown nonwoven web to form a panel having a density between 0.01 and about 0.3 g/cc. The resulting nonwoven web has a thickness greater than about 7 mm.
It is generally accepted in the acoustical insulation art that low density and relatively high thickness meltblown nonwoven webs are needed for sound insulating properties. Therefore, there is a need in the art for a relatively thin sound insulating material which provides sound attenuation properties provided by bulkier materials used in the art.